The fully-discharged or “empty” state of a rechargeable battery constitutes a reference point for determining a number of critical characteristics, including the full capacity of the battery as well as the charge remaining (i.e., state of charge (SOC)) following a period of use or dormancy. The SOC itself is typically applied to determine other important battery characteristics, including the DC resistance (DCR), a measure of wear that may be applied, in turn, to quantify the state-of-health of the battery.
Unfortunately, the conventional approach to establishing a fully discharged battery—discharging a fully-charged battery at a constant current for a predetermined time—tends to yield inconsistent results depending, for example on the discharge current rate and battery temperature, as illustrated conceptually in FIGS. 1A and 1B.